1. Field of the Invention
Embodiments of the invention relate to an insert for a clamping device or gripping apparatus, which is used in particular in the field of oil and gas exploration, wherein such a clamping device or gripping apparatus conducts translational forces and/or torques into a moveable object. Such a moveable object can be a tubular body, including casing, drill pipe, etc. Lengths or stands are added to or detached from such casing or drill pipe strings, for example, during well drilling.
2. Description of the Related Art
In conventional well completion operations, a wellbore is formed to access hydrocarbon-bearing formations by the use of drilling. To drill within the wellbore to a predetermined depth, a drill string having a cutting structure attached to its lower end is often rotated by a top drive or rotary table. After drilling to a predetermined depth, the drill string and drill bit are removed and a section of casing is lowered into the wellbore.
Often, it is necessary to conduct a pipe handling operation to connect joints of casing to form casing strings which extend to the drilled depth. Pipe handling operations require the connection of casing joints to one another to line the wellbore and to form a barrier to the surrounding wellbore. To threadedly connect the casing joints, the casing string must be suspended above the wellbore so that each casing string is disposed coaxially with a casing string previously disposed within the wellbore. The threaded connection must be made up by a device which imparts torque to one casing joint relative to the others, such as a tong or a top drive. The casing string formed of the casing joints is then lowered into the previously drilled wellbore.
It is common to employ more than one string of casing in a wellbore. In this respect, the well is drilled to a first designated depth with a drill bit on a drill string. The drill string is removed. Sections of casing are connected to one another and lowered into the wellbore using the pipe handling operation described above to form a first string of casing longitudinally fixed in the drilled out portion of the wellbore. Next, the well is drilled to a second designated depth through the first casing string, and a second, smaller diameter string of casing comprising casing sections is hung off of the first string of casing. This process is typically repeated with additional casing strings until the well has been drilled to total depth. In this manner, wellbores are typically formed with two or more strings of casing.
As an alternative to the conventional method, drilling with casing is a method often used to place casing strings within the wellbore. This method involves attaching a cutting structure in the form of a drill bit to the lower end of the same string of casing which will line the wellbore. Drilling with casing is often the preferred method of well completion because only one run-in of the working string into the wellbore is necessary to form and line the wellbore for each casing string.
Drilling with casing is typically accomplished using a top drive powered by a motor because the top drive is capable of performing both functions of imparting torque to the casing string to make up the connection between casing strings during pipe handling operations and of drilling the casing string into the formation. Often, the top drive is connected to a gripping head, which is an external gripping device such as a torque head or an internal gripping device such as a spear. An exemplary torque head is disclosed in U.S. Pat. No. 6,311,792 B1, issued on Nov. 6, 2001 to Scott et al., which is herein incorporated by reference in its entirety. An exemplary spear is disclosed in U.S. patent application Publication No. US 2001/0042625 A1, filed by Appleton on Jul. 30, 2001, which is also incorporated by reference in its entirety. The gripping head has a longitudinal bore therethrough through which fluid may flow and grippingly engages the casing string to serve as a load path to transmit the full torque applied from the top drive to the casing string.
In conventional drilling operations as well as drilling with casing operations, drill strings, pipes, and casings, including corresponding pipes or casings connected during the pipe handling operation, are held, torqued, and/or translated by tongs, spiders, elevators, and gripping heads such as torque heads and spears during different stages of a well completion or other wellbore operation. Spiders and elevators are utilized to grippingly engage tubulars, pipes, drill strings, and/or casing strings above the wellbore. A spider is disposed at the surface of the well or at or in a rig floor when utilizing a drilling rig, while an elevator is suspended by bails above the surface of the well to maintain the tubulars, pipes, drill strings, and/or casing strings above the surface of the well during various operations. The spider is used to maintain a tubular, pipe, drill string, or casing string at the surface of the well and prevent it from slipping further into the drilled-out wellbore.
All of the above gripping apparatus may hold pipes, tubulars, drill strings, or casings by means of jaws disposed in these devices. These jaws may have inserts that are interchangeable and conduct translational forces and/or torques into corresponding moveable objects. Such an insert typically comprises a base material and gripping elements. Each gripping element has an object gripping surface with which it engages the corresponding object in order to lift, shift, or rotate the object. In particular, for rotation of the object, considerable clamping or gripping forces are necessary to transmit torque. The corresponding gripping elements are at least partially embedded in the base material and may be fixed within the base material during vulcanization.
A prior art clamping device includes strip-like gripping elements extending parallel with the longitudinal axis of the object to be gripped. Such inserts are sufficient for lifting or holding corresponding objects. However, if these inserts are used for rotating the object, it is possible that the corresponding gripping elements may tilt away under heavy load produced while transmitting torque to the object. Moreover, such inserts can cause undesired indentations or markings on the surface of the object to be clamped such that this surface undergoes increased corrosion. These indentations and markings are, in particular, caused during starting of the rotation when the clamping power has to be increased to stop relative movement between the jaws and the object being clamped.
Prior art gripping apparatuses cause scarring and/or marking of the object being grippingly engaged when imparting torque to the object. The scarring and/or marking increases damage to the object, thus possibly impairing the effectiveness of the object in the well operations and increasing the incidence of failure of the pipe, e.g., casing or other tubular body, within the wellbore. Additionally, the scarring and/or marking may increase corrosion along the pipe's surfaces.
There is a need, therefore, for an insert for a clamping device with which it is possible to transmit a higher torque, even when having a small gripping area, and leaving fewer indentations or markings on the surface of an object to be clamped. There is also a need for a gripping apparatus which minimizes damage to an object being grippingly engaged, even while maintaining the effectiveness of the frictional engagement with the object, and even while imparting torque to or linearly translating the object.